Over the last fifty years, approaches toward providing animal nutrition have changed. No longer are the animals fed whatever grain or forage may be available. Instead, the diets of animals are closely monitored for total nutrition value, and for cost. The animal on the diet is monitored, for quality and performance characteristics, and for the environmental impact of the waste from the animal. The information gathered is employed to adjust the feed to increase nutrition value of the feed and the animal performance characteristics while decreasing the cost and environmental impact.
Cereals and fats are used in feeding programs for nonruminants such as swine and poultry to provide a nutritional source of calories. The ratio of cereals to supplements, such as vitamins, minerals and fats, have changed across years in an attempt to maximize feeding efficiency of the animals. The feeding efficiency (the feed conversion ratio) or how much feed is required to produce one pound of animal weight is determined by a combination of matching the genetic potential of the animal, and the nutrients supplied to the animal. As the feed conversion ratio has risen due to genetic enhancements, the mineral nutrient requirements in the feed have risen to assure a complete and heathy diet.
Since an animal's ability to feed limits the amount of nutrients and calories it can consume, the feed industry has had to develop ways to make feeds that are more highly caloric. To increase the caloric density of the feed, producers have added fat to the feed. Fat has often been added to the feed in the form of a liquid. Fat has the advantage of supplying calories to each mouthful of feed. However, adding fat to feed has some disadvantages such as costs, added labor and technical difficulties with automatic feeding systems. Additionally, the fat is often of poor quality, thus reducing the overall quality of the feed.
To reduce the use of liquid fat in feeds, the industry has tried increasing the oil content of the grain used in the feeds. The Dupont company has developed and commercialized high oil corn as a method for increasing the oil content of feed. Other companies have developed corn that has more oil than no. 2 yellow dent corn but less than Dupont's high oil corn. High oil and elevated oil corn is herein alternatively referred to as oil burdened corn. This extra oil in the corn reduces and may eliminate the need for the addition of the liquid fat to the feed.
Traditionally, oil burdened corn has been thought to contain increased level of phytic acid, as compared with levels in No. 2 yellow dent corn. Raboy et al (Journal of Heredity 1989: 80: 311–315) have reported however, that there is an apparent negative relationship between selection for oil and total phytic acid, phytic acid phosphorus and phosphorus per kernel, per germ and per endosperm of Illinois High Oil and Low Oil lines, as opposed to the previously expected apparent positive relationship on a concentration basis (i.e., mg constituent per g kernel, germ or endosperm). Raboy explains that the discrepancy between total contents per organ and concentration per organ results from the large divergence in organ dry weights exhibited between the Illinois High Oil (IHO) and Illinois Low Oil (ILO) seed used in his study; IHO germ being about twice the dry weight of ILO germ and ILO endosperm having nearly three times the dry weight of IHO endosperm. In contrast to this trend for high oil being linked to lower phytic acid, Raboy also reports a consistent positive relationship between increasing protein selection and increasing amounts of phytic acid, phytic acid phosphorus and phosphorus. Thus, there is an apparent positive relationship between selection for protein and total phytic acid, phytic acid phosphorus and phosphorus per kernel, per germ and per endosperm of illinois high protein and low protein lines. This was maintained even when the data are expressed on a concentration basis (i.e., mg constituent per g kernel, germ or endosperm). Thus selection for protein and oil appears to divergently affect phytate content in seed.
As reports suggest an average increase of 0.38% protein with each 1% increase in oil (Han Y. Et al., 1987 Poultry Science 66:103–111; Keshararz, Poultry Pointers, pp6–7), it is uncertain from the art whether grains containing high oil, high protein and low phytic acid could be produced (Brewer, “Optimum® High Oil Corn Improves Poultry Rations” Poultry Digest, February/March 1998 pp30–31). Brewer states that while high oil corn is available as of 1998, varieties which are high in oil, high in protein and high in digestible phosphorus (i.e., low in phytic acid phosphorus), have yet to be developed.
The concentration of phytic acid in grain-based diets has long been of concern to humans and animal nutritionists, because evidence has shown that phytic acid acts to form insoluble salts with nutritionally important minerals that subsequently are not absorbed in the intestine. Phytic acid (myo-inositol 1,2,3,4,5,6-hexakis (dihydrogen phosphate)) is a form of phosphorus (P) in seeds which is stored in the form of phytate salts. Phytate salts have a negative nutritional impact on the animal because phosphorus bound to phytate is not available to the animal as a source of nutrition. Moreover, the animal does not retain the minerals such as Ca, Zn and the like and these needed minerals are excreted. Finally, the animal waste contain phytate P which then contributes to the surface and ground water pollution. If the grain is used for milling purposes then the milling by-products contain phytate P which then contributes to the surface and ground water pollution.
Swine, for example, lack the digestive enzyme (phytase) required to cleave the phosphorus from the phytate molecule and thus can not readily use phytate-phosphorus. Increasing the availability of phosphorus by elimination of the phytate salts binding the phosphorus would enable a reduction in dietary total phosphorus content without jeopardizing the animal's health or production performance. Increasing the bioavailability of phosphorus results in a lower phosphorus content in the swine wastes, which is environmentally desirable.
In one attempt to release a portion of the phytate P present in maize and soybean meal the feed industry has added microbial phytase to the feed of animals. This method of dealing with phytate in the grain appears to partially decrease the phosphorus excreted by the animal. This research apparently led to further methods of degrading phytate in feed. One method includes adding an enzymatic cocktail and Aspergillus niger mycelium to feed. These components function to hydrolyze phytate present in the corn-soybean diet. Turkeys fed the enzymatic cocktail and the fungal mycellium showed enhanced performance and retention of P and Ca. These feed studies were planned to dephosphorylate the corn and soybean based feeds prior to consumption by the animal and thus reduce the P excreted. This method of dealing with phytate in the grain has the distinct disadvantage of adding labor and cost to the feed.
Mogen, in U.S. Pat. No. 5,593,963, describes production of a temperature stable phytase enzyme from Aspergillus in a corn or soy seed through genetic engineering techniques. The genetically produced phytase was designed to reduce the phytic acid content in animal feed by degrading the phytic acid being released from the grain and thus decrease the level of phosphorus excreted by the animal.
Low phytic acid mutant yellow dent corn seeds have been produced by Raboy and described in U.S. Pat. No. 5,689,054. This patent describes the discovery of a single gene, nonlethal lpa1 mutants in maize that cause the reduction of kernel phytic acid phosphorus by up to 95% over the wildtype phytic acid phosphorus levels. Raboy notes that while the mutants of his invention are phenotypically very similar to the wild-type, the mutants would need to be introduced in to a breeding program in order to introduce the low phytic acid trait in to a commercial line. Moreover, Raboy explains that the low phytic acid maize mutants of his invention are characterized by a small kernel dry weight reduction which could result in a reduction in productivity and that homozygous mutants may reduce or eliminate agronomically important characteristics. As Raboy et al (Journal of Heredity 1989) has indicated that divergent selection for high protein consistently produces higher phytic acid lines, it is unclear how the lpa1-R and lpa2-R mutations described in the Raboy patent in yellow dent corn will interact with genes for high-protein and oil-burdened corn seed. Thus one could not have predicted with certainty whether it would have been possible to maintain a high-protein oil burdened seed in combination with a low phytic acid mutant.
Although the feed industry has addressed both the need for more energy in the feed and the need for less phytate-phosphorus, the feed industry has not addressed the need for a method of providing, in a cost efficient manner, both the high nutrient density (i.e., high protein and high oil) and the low phytic acid in feed. There is a need to reduce the amount of phytate salts formed in feed and increase the amount of energy in feed without having to add phytase and liquid oil to feed. There remains a need, which has not been addressed, for a grain having a combination of increased protein and oil burden and low phytic acid levels. To reduce feed costs in animal production requires a nutritionally dense material that is cost-effective and environmentally friendly. Additionally, there remains a need for a feed containing an oil burdened, protein laden corn with low phytic acid levels which can be used for milling or for feed purposes.